1. Field of the Invention
The present invention relates to a motor. More particularly, the present invention relates to a new structure of a motor, which can be operated at a variable speed by demagnetizing or magnetizing some of magnets applied to a rotor and can obtain high efficiency by concentrating an amount of magnetic flux.
2. Background Art
In general, in order to simultaneously obtain a variable speed operation and high efficiency of a motor, various structures and forms of motors have been proposed.
Representatively, there are a variable flux memory motor (VFMM) (hereinafter, called “prior art 1”) and a motor disclosed in Japanese Patent Laid-open No. 2009-112454 (hereinafter, called “prior art 2”).
A rotor of the variable flux memory motor according to the prior art 1 is basically similar with a brushless DC electric motor (BLDC motor) of a spoke type. The motor is a motor that permanent magnets are demagnetized from a narrower part thereof due to a difference in thickness of the permanent magnets when a negative d-axis current flows to a d-axis which is a magnetic flux generation axis of a stator. The motor is operated at a variable speed by demagnetizing and magnetizing the permanent magnets based on the above principle.
The motor according to the prior art 2 is basically similar with an outer-rotor type BLDC motor of a salient pole concentrated winding structure. The motor is characterized in that two kinds of magnets with different coercive forces are embedded in a rotor core in such a way as to be arranged in a circumferential direction in turn to thereby form opposite poles. That is, the rotor core has holes for embedding a first magnet and a second magnet therein and protrusions formed on an inner face of the rotor core. Accordingly, the motor according to the prior art 2 has several problems in that the rotor core is complicated in structure and manufacturing costs are increased. Particularly, the first magnet is a neodymium (Nd) magnet, and it is the factor in an increase of manufacturing costs.
In order to solve the above problems of the prior arts, the inventors of the present invention propose a new structure of a motor that includes a rotor of a modified spoke type and a stator of a salient pole concentrated winding structure to thereby concentrate an amount of magnetic flux, to cause a high performance enhancement, and to reduce manufacturing costs.